Optical fiber measurements of particle concentration in dense suspensions: calibration and simulation.

A fiber-optic sensor that measures the particle volume fraction in dense suspensions is calibrated against a quantitative capacitance probe. For homogeneous, dense, random suspensions of smooth, monodisperse, transparent dielectric spheres, the calibration is simulated by using a ray-tracing Monte Carlo algorithm that predicts systematic uncertainties of the sensor's output, the extent of its measurement volume, and the effects of changing its optical properties. The simulation shows that the output and accuracy of the sensor increase with a decreasing sphere diameter and with an increasing N.A. of the fiber. The output also increases when the ratio of the indices of refraction of the sphere and the suspending medium is increased. For small particles the measurement volume scales as the average interparticle distance.